There have been manufactured and marketed battery-type wristwatches that hold primary batteries such as silver battery or lithium battery. A quartz wristwatch that runs accurately for one to three years without requiring winding of a spring has been widely distributed because of the ease of carrying the watch and the low price of the watch. However, depending on the country, watch batteries are sold only at certain places, and battery prices and battery changing charges are high. Therefore, when a battery is drained, the watch user cannot change the battery, and the watch remains stopped. Further, abandonment of drained batteries leads to the abandonment of valuable metal resources or the abandonment of toxic mercury, which is harmful to the global environment. The recovery of spent batteries requires much cost, which is a serious issue to be overcome by watchmakers, watch users, and the autonomous communities that carry out refuse disposal.
A watch that carries out the time holding operation based on collecting energy from the environment and storing the energy is one of most effective methods to solve the above problems. However, a compact secondary battery has an operating life of only a few months, in the watch, even when the battery is charged fully. Therefore, in order to realize an operating life of at least one year, it is necessary to use either a thick watch by using a large battery or a watch having no second hand to save power. Consequently, to realize a mechanism of an electric timepiece consuming low power is an important issue for both the electric timepiece that employs a primary battery and an electric timepiece that employs a secondary battery.
There is a watch in the market that employs a system of holding time with only an electric counter circuit by stopping the hands of time display in order to save power, and driving the hands after the battery is charged. However, this watch displays time inaccurately until the battery is charged sufficiently. Therefore, this watch does not satisfy users' requirement for a constant display of accurate time.
It is possible to consider a mechanism that uses a plurality of wheel trains including a wheel train which drives a second hand and a wheel train which drives an hour hand, a minute hand, and a calendar, and that stops only the driving of the second hand when the stored energy is low. However, as this mechanism uses two motors, the watch becomes large and has a large weight, which leads to a cost increase, and results in an expensive watch. Therefore, it has been difficult to employ this mechanism for a compact thin practical watch available at a low price.
Therefore, the present invention realizes the mechanism of a plurality of wheel trains driven by one motor instead of the mechanism of a plurality of wheel train driven by two motors. When one motor is used to drive a plurality wheel trains, an increase in volume, an increase in weight, and an increase in cost can be avoided. Further, the save power operation can be carried out based on the charged capacity.